This invention relates to a method and apparatus for employing emergency power in a turbofan engine.
Many commercial aircraft employ ram air turbines (RAT) as sources of emergency power in conditions where all main propulsions engines have failed. The RAT deploys from the aircraft fuselage and turbine blades unfold so that they may be driven by the aircrafts' forward motion. The turbine drives a hydraulic pump and/or electric generator. The RAT adds weight and cost to the aircraft. RATs must be checked periodically to ensure their operability since they are not deployed during normal aircraft usage.
Turbofan engines have been designed in which the fan is used to drive a generator in emergencies. In a turbofan engine, a flow path is arranged in the fan duct formed between core and fan nacelles. When the engine loses power, the fan rotationally drives a generator during a windmilling condition in which the fan is rotationally driven by airflow through the fan duct from the aircraft's forward motion. A large generator is required to provide sufficient power at the relatively low rotational speeds of the fan during the windmill condition. The large generator adds weight and cost to the turbine engine. Furthermore, the wide variation in the fan speed and the net pressure drop through the fan duct makes designing and efficient generator difficult.
What is needed is a turbine engine that enables a smaller generator to be used for emergencies.